Lymph nodes are oval or bean-shaped organs that lie,often in groups,along the length of lymph vessels. The lymph drains through a number of nodes,before returning to the venous circulation. These nodes vary considerably in size: some are as small as a pin head and the largest are about the size of an almond.
Lymph nodes have an outer capsule of fibrous tissue that dips down into the node substance forming partitions,or trabeculae. The main substance of the node consists of reticular and lymphatic tissue contains many lymphocytes and microphones.
As many as four or five afferent lymph vessels may enter a lymph node while one efferent vessel carries lymph away from the node. Each node has a concave surface called the hilum where an artery enters and a vein and the efferent lymph vessel leave.
The large numbers of lymph nodes situated in strategic positions throughout the body are arranged in deep and superficial groups.
Lymph from the head and neck passes through deep and superficial cervical nodes.
Lymph from the upper limbs passes through nodes situated in the elbow region,then through the deep and superficial axillary nodes.
